1. Field of Invention
The invention relates to a range switchover apparatus for use in switchover of a running range of an automatic transmission.
2. Description of Related Art
Conventionally, a range switchover apparatus for switchover of a running range of an automatic transmission comprises a manual valve in the automatic transmission, and a shift lever connected to the manual valve by a shift cable and provided in a vehicle interior. The range switchover apparatus is constructed such that a driver operates the shift lever to thereby switch over the manual valve via the shift cable. However, a requirement has been created to permit increased freedom for the location where the shift lever is installed, as a result of recent increases in the freedom in vehicle interior design for automobiles and because of an increase in the types of vehicle derived from the same platform.
A range switchover apparatus, which meets with such demand, is disclosed in Japanese Patent Laid-Open No. 190180/1995. With such a range switchover apparatus, a motor is used to actuate a manual valve to perform switchover of the running ranges.
However, conventional range switchover apparatuses have never taken any measure to meet secular change due to a long term use of the motor. Therefore, there is the possibility that a change in rotational speed of the motor extends or shortens the time required for the switchover of ranges, thereby giving an uncomfortable feeling to a driver.
The invention has its object to provide a range switchover apparatus capable of surely performing a switchover of a switchover means while preventing secular change from causing a change in the rotational speed of a motor for driving a switchover means of an automatic transmission.
The above-mentioned problem is solved by a range switchover apparatus for automatic transmissions, comprising a range switchover means operating unit capable of switching over a switchover means, which switches over a shift range, among respective shift positions (P, R, N, D, L), a drive motor for driving the range switchover means operating unit, a measuring unit for measuring a time, during which the drive motor causes the range switchover means operating unit to switch over between predetermined shift positions (P, R, N, D, L), a rotation control unit for controlling the rotational speed of the drive motor, a correcting unit for correcting the rotational speed by the rotation control unit so that when a time measured by the measuring unit differs from a target time in a predetermined range, the measured time becomes the target time, and a storage unit for storing the rotational speed corrected by the correcting unit.
The invention has a feature in the range switchover apparatus for automatic transmissions, such that the target time is one set in accordance with an environmental condition, the rotation control unit controls the rotational speed of the drive motor on the basis of a duty ratio of the drive motor, and the correcting unit compares the measured time and the target time with each other to correct the duty ratio so as to make the duty ratio large when the measured time exceeds the target time and to correct the duty ratio so as to make the duty ratio small when the measured time is short of the target time.